DIY ECG and Pulse Oximeter with LM324 OpAmp (2 of 2)

This is a smaller part of a bigger project. http://www.SWHarden.com It's a single LM324 quad operational amplifier using all 4 amps: (1) virtual ground, (2) preamplifier, (3) lowpass filter, (4) final amplifier and second lowpass filter. It doubles as a pulse oximeter (near rail-to-rail swing at 12V and 5V) with a phototransistor, and an ECG (about 0.5 V output). IMPROVED PROJECT WITH AD8232: https://youtube.com/watch/sP_-f5nsOEo